Respiratory Syncytial Virus (RSV) is a member of the paramyxovirus family, which consists of mostly highly contagious non-segmented, negative polarity RNA viruses that spread through the respiratory route. RSV disease is the leading cause of virus infection-induced death among children below one year of age (Thompson W W, et al. (2003) JAMA 289(2):179-186) and can be life-threatening to the elderly and the immunocompromised (Elliot A J, et al. (2008) Expert Rev Vaccines 7(2):249-258; Ebbert J O, et al. (2005) Respiration 72(3):263-269). Reinfection with RSV can occur throughout life, but infants born prematurely, with bronchopulmonary dysplasia or a congenital heart defect are at highest risk of developing severe disease (Mahadevia P J, et al. (2012) J Med Econ 15(5):987-996). In a typical case, initial RSV infection of airway epithelia cells is followed by rapid spread from the nasopharynx to the lower airways that can affect respiratory function through excessive mucus, necrotic epithelial debris, and inflammatory cells obstructing the airways (Aherne W, et al. (1970) J Clin Pathol 23(1):7-18; Lugo R A, et al. (1993) Clin Pharm 12(2):95-116).
Attempts to develop an effective RSV vaccine have been fruitless thus far, since the virus is poorly immunogenic overall and neutralizing antibody titers wane quickly post infection. Although ribavirin was approved for RSV treatment, clinical use is minimal due to efficacy and toxicity issues (Anderson L J, et al. (1990) J Infect Dis 161(4):640-646; Hall C B, et al. (1993) Pediatrics 92(3):501-504). The humanized neutralizing antibody palivizumab is used for immunoprophylaxis of high-risk pediatric patients, but high costs prohibit broad scale implementation (Mahadevia P J, et al. (2012) J Med Econ 15(5):987-996; Broor S, et al. (2007) PLoS One 2(6):e491; Mahadevia P J, et al. (2012) Arch Pediatr Adolesc Med 166(10):968-969; author reply 969-970; Kamal-Bahl S, et al. (2002) Arch Pediatr Adolesc Med 156(10):1034-1041; Hampp C, et al. (2011) Arch Pediatr Adolesc Med 165(6):498-505).
Clinical disease associated with infection by several paramyxoviruses such as mumps virus or measles virus (MeV) originate predominantly from immunopathogenic effects, which makes therapeutic treatment challenging, since viral replication is typically immune-controlled and titers decline when symptoms become manifest (de Vries R D, et al. (2012) Curr Opin Virol 2(3):248-255; Griffin D E (2010) Immunol Rev 236:176-189). In the case of RSV infection; however, several studies have suggested that pathogenesis is not the result of host immunopathology alone. Rather, higher viral loads were recognized as a predictor for severe lower respiratory infection in infants (DeVincenzo J P, et al. (2005) J Infect Dis 191(11):1861-1868), and RSV titers on day three of hospitalization were indicative for increased need for intensive care in hospitalized children less than two years old (El Saleeby C M, et al. (2011) J Infect Dis 204(7):996-1002). These observations suggest that efficacious therapeutics given early to hospitalized children may improve downstream morbidity and reduce immunopathology, opening a window for improved disease management and making RSV a premier target for drug discovery campaigns.
However, large scale screening campaigns to identify novel therapeutic candidates against RSV have been compromised thus far by the lack of appropriate reporter strains. Moreover, previous anti-RSV drug discovery campaigns have yielded several structurally distinct, highly potent, small-molecule entry inhibitor classes that often lead to drug resistant escape mutations.